Recently, an endoscope device having a function of photographing spectroscopic image (spectral endoscope device) has been proposed. By using such a spectral endoscope device, it is possible to obtain information concerning spectral property (e.g., reflection spectrum) of a biological tissue such as a mucous membrane of a digestive organ. It is known that the reflection spectrum of a biological tissue reflects information concerning types or densities of components contained in the vicinity of a surface layer of a biological tissue being a measurement target. Specifically, it is known that an absorbance calculated from the reflection spectrum of a biological tissue equals to an absorbance obtained by linearly superimposing absorbances of a plurality of substances that compose the biological tissue.
It is known that composition and amount of substances in a lesion biological tissue differ from those in a healthy biological tissue. It is reported in many of the earlier studies that abnormalities of lesions represented by such as cancer are particularly deeply related to a condition of blood, especially to an overall amount of blood or oxygen saturation. Qualifying and quantifying two focused biological tissues by using spectroscopic feature values within the visible range that the two focused biological tissues have is a frequently used method in the field of spectrographic analysis. Therefore, it is possible to estimate existence of some kind of lesions in a biological tissue by comparing a spectral characteristic of blood in a biological tissue that includes lesions with a spectral characteristic of blood in a biological tissue that does not include lesions.
A spectral image is composed of a series of image information taken using light of different wavelengths, and more detailed spectral information of a biological tissue can be obtained from the spectral image having higher wavelength resolutions (i.e., larger number of wavelengths used to acquire image information). Patent Document 1 discloses an exemplary configuration of a spectral endoscope device which acquires spectral images in a wavelength range of 400-800 nm at 5 nm intervals.